1. Field of the Invention
This invention relates to a process for preparing an electrical connecting member to be used in connecting electrically electrical circuit parts to each other.
2. Related Background Art
In the prior art, as the method for connecting electrically electrical circuit parts to each other, the wire bonding method, TAB (Tape Automated Bonding) method, etc. have been known. However, in these methods, there have been drawbacks in that they cannot correspond to the increase of connecting points between the both electrical circuit parts, and are also high in cost. In order to solve such drawbacks, it has been known in the art to connect electrical circuit parks to each other by use of an electrical connecting member having a constitution equipped with a plurality of electroconductive members insulated from each other in an insulating holding member (Japanese Laid-open Patent Applications Nos. 63-222437, 63-224235, etc.).
FIGS. 1A and 1B illustrate schematically such electrical connecting member and electrical connection between the electrical circuit parts by use thereof, and in the Figures, 31 shows the electrical connecting member, and 32, 33 show the electrical circuit parts to be connected. The electrical connecting member 31 is constituted of a plurality of electrical members 34 comprising a metal or an alloy equipped in the holding member 35 comprising an electrically insulating material with the electroconductive members 34 being electrically insulated from each other, and has one end 38 of the electroconductive member 34 protruded on one side of the electrical circuit part 32, and the other end 39 of the electroconductive member 34 protruded on the other side of the electrical circuit part 33 (FIG. 1A). To the connecting portion 36 of one electrical circuit part 32 one protruded end 38 of the electroconductive member 34 is bonded by deformation according to pressure adhesion, thermal pressure adhesion, etc., and to the connecting portion 37 of the other electrical circuit part 33 is the other protruded end 39 protruded of the electroconductive member 34 is bonded by pressure adhesion, thermal pressure adhesion, etc. (FIG. 1B). Thus, the corresponding connecting portions 36, 37 of the electrical circuit parts 32, 33 are connected to each other.
With such an electrical connecting member, there are advantages as shown below.
(1) By making the size of the electroconductive member smaller, the connecting portion of the electrical circuit part can be made compact, and, the number of connecting points can be increased, whereby higher density connection mutually between electrical circuit parts can be made. PA1 (2) Even for electrical circuit parts with different thickness, the height of the electrical circuit parts can always be made constant by varying the thickness of the electrical connecting member, whereby multi-layer connection can be easily done to enable higher density practical mounting. PA1 (3) By making the protruded height of the electroconductive member to be connected with the connecting portion of the electrical circuit part large, even if the connecting portion of the electrical circuit is partly sunken from the surface it can be stably connected, whereby it is possible to easily connect electrical circuit parts having complicated shapes to each other. PA1 (4) Since the heat generated from the electrical circuit parts is dissipated through the holding member of the electrical connecting member, the electrical characteristic change is extremely small. Also, because of excellent heat dissipating characteristic, the influence of heat fatigue is small and reliability is also high. PA1 (5) Since the connecting length mutually between the electrical circuit parts is short, impedance can be reduced and speed-up of electrical parts can be effected. PA1 (6) Since the amount of the electroconductive member to be used in the electrical connecting member is small, the cost is low even when an expensive metal may be employed. PA1 (7) Since the connecting portion of the electrical circuit part is formed into an alloy through the electrical connecting member, there is no variance of contact resistance and reliability of connection is high.
As the process for preparing such electroconductive member, there is one proposed in Japanese Patent Application No. 63-133401. In the following, this preparation process is described briefly by referring to FIGS. 2A-2F showing its steps schematically.
First, a substrate 51 comprising a metal sheet such as copper plate, etc. is prepared (FIG. 2A), and on the substrate 51 is coated a nega-type photosensitive resin 52 by a spin coater, which is then prebaked at a temperature around 100.degree. C. (FIG. 2B). Through a photomask forming a predetermined pattern (not shown), light is irradiated (exposed) on the photosensitive resin 52, followed by developing. At the irradiated portion, the photosensitive resin 52 remains, while at the unirradiated portion, the photosensitive resin 52 is removed by the development, whereby a plurality of holes 53 are formed (FIG. 2C). After curing the photosensitive resin 52 by elevating the temperature to 200.degree. to 400.degree. C., the substrate 51 is dipped in an etchant to effect etching, thereby forming concavities 54 communicated to the holes 53 on the substrate 51 (FIG. 2D). Next, by application of gold plating with the substrate 51 as the common electrode, gold 55 is filled in the holes 53 and the concavities 54, and gold plating is continued until bumps are formed (FIG. 2E). Finally, the substrate 51 is removed by etching to prepare an electrical connecting member 31 (FIG. 2F).
In the electrical connecting member 31 thus prepared, the old 55 constitutes the electroconductive member 34, and the photosensitive resin 52 constitutes the holding member 35. The electroconductive member 34 consists of the portion 34a embedded within the holding member 35 (hereinafter called the columnar portion 34a) and the portions 34b protruded from the both surfaces of the holding member 35 (the ends 38, 39 in FIG. 1A, hereinafter called the bump portions 34b).
The bumps 38, 39 formed at both ends of the above electroconductive member 34 must to be surely connected to the connecting portions 36, 37 of the electrical circuit parts 32, 33 on the both sides.
Ordinarily, when the electroconductive member 34 of the above electrical connecting member 31 is connected by alloy formation with the electrical circuit parts 32, 33, the connecting portions 36, 37 of the electrical circuit parts 32, 33 are bonded by pressurization, heating, and the bumps 38, 39 of the electroconductive member 34 will be deformed as accompanied with such pressurization, heating treatment to embed the voids at the connecting interface to effect separation from the impurity coating such as oxides, etc., whereby the electroconductive member 34 and the clean surfaces of the electrical circuit parts 32, 33 come into contact with each other, whereby connection is effected metallurgically.
Through such connection by pressure adhesion or thermal pressure adhesion, the bumps 38, 39 are deformed respectively to be spread in the lateral direction. If the deformation amount differs between the bumps 38 and 39 on the both sides, or the bonding state differs on the surfaces on both sides of the photosensitive resin 35, reliability of connection will be lowered undesirably.
What is important in effecting connection is control of the protruded height of the bump from the photosensitive resin 35. The bump 38 is formed by carrying out plating treatment of the electroconductive member 34 as raised up on the upper surface of the photosensitive resin 35. However, if variance of its height occurs, and also if it is desired to be formed high to some extent, the bump will be spread in the circumferential direction, whereby the adjoining bumps may sometimes contact each other to cause short circuit to occur.
Accordingly, the shapes and sizes (protruded height, area, volume) of the bumps 38, 39 formed by plating treatment together with the electroconductive member 34 are required to be made the same. However, in the preparation steps as described above, the bump 39 is formed within the framework subjected to etching in the substrate 51, namely within the concavities 54, while the bump 38 is formed in the form raised up on the upper surface of the photosensitive resin 52. Therefore, the shape and the size of the bump 39 is influenced by the progress extent of etching of the concavities 54, while the shape and the size of the bump 38 are influenced by the progress extent of the plating treatment, and therefore it is very difficult to control these progresses to the same level. Particularly, control of etching is difficult as compared with control of plating treatment, and it is difficult to form concavities 54 with constant shape and size for every etching. Further the bump 38 is influenced by the shape of its concavity 54 to form the central portion of the bump in concave, or convex shape or even in flat shape, whereby there is the problem that it is difficult to control the shapes and the sizes of the bumps to be identical or to be in any desired shape. As a consequence, connection for the electrical circuit parts on both sides cannot be effected uniformly, whereby there has ensued the technical problem that reliability of connection is lowered.
In bonding the electroconductive member of such electrical connecting member to the connecting portion of the electrical circuit part by pressure adhesion or thermal pressure adhesion, of 2- to 10-fold pressurization of conventional pressure adhesion or thermal pressure adhesion is required.
However, when a brittle material such as Si chip, etc. is employed for the electrical circuit part, the pressurizing force may become excessively great, whereby the electrical circuit part may sometimes be destroyed. Also if the heating temperature is too high, there is the problem that the function of the electrical circuit may be damaged.
However, there has not yet been proposed an effective process for preparing an electrical connecting member having a constitution which will not be destroyed by the pressurizing force during pressure adhesion or thermal pressure adhesion while controlling the bump shapes to be identical, or shaped as desired, and yet capable of accomplishing higher, finer connection between electrical circuit parts at high efficiency end low cost.